Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $147.55   3.359%   $152.5062   $152.51   $152.50   $152.50  
  Purchase #2 $67.62   11.823%   $75.6147   $75.61   $75.60   $75.60  
  Purchase #3 $11.50   4.267%   $11.9907   $11.99   $12.00   $12.00  
  Purchase #4 $130.91   3.683%   $135.7314   $135.73   $135.75   $135.70  
  Purchase #5 $249.82   5.307%   $263.0779   $263.08   $263.10   $263.10  
  Purchase #6 $76.27   11.123%   $84.7535   $84.75   $84.75   $84.80  
  Purchase #7 $102.68   12.312%   $115.322   $115.32   $115.30   $115.30  
  7 purchase totals = $786.35       $838.9964   $838.99   $839.00   $839.00